1. Field of the Invention
This invention relates to a photoconductive process of coating a photoconductive member with a resin to form a negative image suitable for use in electrographic copying, such as xeroprinting.
2. State of the Prior Art
Photoconductors have long been used to print a large number of copies from a persistent image formed thereon.
To improve upon the quality of images formed by processes such as xerography, one technique has been to form, by photoconductography, a coating of an ionic electrolyte over a photoconductor, the electrolyte being electrically attracted to the oppositely biased-photoconductor surface upon imagewise exposure of the interface. The result is the formation of a negative image which can be used to form a positive image by applying a developer to the areas of the photoconductor not imagewise covered by the electrolyte. A representative patent illustrating this approach is U.S. Pat. No. 3,178,362.
Such photoconductive process has been limited, not surprisingly, to the use of electrolytes having a net charge which is opposite in sign to the bias imposed on the photoconductor. In those instances in which the preferred resins are cationic resins, such as quaternary ammonium compounds described in U.S. Pat. Nos. 3,011,918 and 3,228,700 the process thus has been limited to an application of a negative polarity only to the photoconductor. This in turn has limited the selection of photoconductor materials to those which work well in photoconductography when given a negative potential.
However, recent discoveries have led to novel photoconductor materials which, along with the more conventional photoconductors such as selenium and cadmium sulfide, work best when biased with a positive potential. Representative of such materials are certain of the "aggregate" and "multiactive" photoconductive elements, as described, respectively, in Light U.S. Pat. No. 3,615,414 and in commonly-owned U.S. application Ser. No. 534,979, filed on Dec. 20, 1974, by M. A. Berwick et al, entitled "Multi-Active Photoconductive Element I." Thus, a process which will permit photoconductography to be accomplished with a positive potential applied to the photoconductor will make a more efficient use of such photoconductive materials. Heretofore, it has been considered that such a potential would be totally inoperative when the electrolyte is cationic in nature, due to the like charges repelling each other.
Patents relating generally to the background of photoconductography include U.S. Pat. Nos. 3,010,883, 3,106,155, 3,172,826, 3,288,770, 3,425,829, 3,550,153, 3,676,116, 3,676,215 and 3,692,516, and British Pat. No. 1,006,115.